Biochar and nitrogen fertilizer promote rice yield by altering soil enzyme activity and microbial community structure

<p><span>Biochar can significantly change soil properties and improve soil quality.</span> <span>However, the effects of long-term combined application of biochar (B) and nitrogen (N) fertilizer on relationships between soil enzyme activity, microbial community structure and crop yield are still obscure. We characterized these relationships in a long-term (8 years) field experiment with rice, two biochar rates of 0 and 13.5 t ha^-1 year^-1 (B0 and B) and two N fertilizer rates of 0 and 300 kg N ha^-1 year^-1 (N0 and N).</span><span> The repeated, long-term combined applications of biochar and N fertilizer significantly increased microbial biomass carbon and nitrogen (MBC and MBN), but biochar decreased the abundance of total bacteria, fungi, actinomycetes, Gram-positive and Gram-negative bacteria as well as the amount of total phospholipid fatty acids. </span><span>The activity of leucine aminopeptidase (LAP) </span><span>decreased significantly in the biochar-amended and N fertilized treatment, but</span><span> the LAP activity either remained unchanged or increased with biochar amendment at N0. The relative abundance of bacterial phylum <em>Chloroflexi</em> was increased in the combined biochar and N fertilizer treatment. The changes in soil organic matter and the activity of α-1,4-xylosidase were the major properties influencing soil bacterial community composition, whereas the structure of fungal community was governed by MBC, MBN and LAP activity. In addition, long-term biochar and N fertilizer applied together significantly increased rice yield (more than biochar and nitrogen fertilizer applied alone). Yield</span> <span>was significantly positively correlated with LAP activity, but significantly negatively correlated with the relative abundance of Chloroflexi. In conclusion, long-term biochar and nitrogen fertilizer applications increased rice yield, which was associated with altered soil microbial community and enhanced activity of some enzymes.</span></p>